Handshake: Design-by-Contract

Handshake, currently in version 0.3.0, is an informal design-by-contract system written by Brian Guthrie in pure Ruby. It's intended to allow Ruby developers to apply simple, clear constraints to their methods and classes.

Handshake is definitely welcome alongside the ever-increasing number of test-driven and behavior-driven design/development based tools, such as RSpec and test/spec.